Method of roasting ore



Jan. 4, 1938. E. J. MULLEN 2,104,091

METHOD OF ROASTING ORE Filed June 2'7, 1935 INVENTOR E d 140?? J Mu llen ATTORNEY Patented Jan. 4, 1938 METHOD OF ROASTING ORE Edwin J. Mullen, New Rochelle, N. Y., assignor to General Chemical Company, New York,

N. Y. a corporation or New York Application June 2'1, 1935, Serial No. 28,599

1 Claim.

. This invention is directed to methods-and apparatus for roasting metal sulfides, and more particularly for roasting finely divided sulfides to desulfurize the same and to produce sulfur dioxide for use in the manufacture of sulfuric acid,

or for any other purposes desired.

The nature of the invention, and the objects and advantages thereof may be fully understood from a consideration of the-following description taken in connection with the accompanying drawing showing in Fig. l a vertical section of a preferred form of'burner for carrying out the improved process, and in Fig. 2 a-vertical section of an injector.

Referring to the drawing, l designates a shaft burner, comprising a steel shell or casing H within which is placed the furnace lining l2, constructed of suitable refractory material such as flrebrick and defining an unobstructed roasting .chamber M of cylindrical horizontal crosssection and having a vertical dimension preferably substantially in 'excess of the diameter. The upper part of the combustion chamber is closed off by a crown |5 the top side of which forms a. drying or preheating hearth ll. The shell projects upwardly beyond the crown l5 .and carries a steel framework l8 which in turn supports ore feedingand rabblingmechanism for the drying hearth.

The surface of hearth i1 is slightly coneshaped and slopes downwardly toward the shell of the burner. Lying above the hearth are rabble arms l9 having downwardly projecting plows 20 pitched to work sulfides gradually toward the circumference of the drying hearth. Arms l9 are rotated by a motor 22 through shaft 23 supported in bearings so as to maintain the lower ends of the plows 20 spaced with respect to the surface of drying hearth H. An ore bin ,24 mounted on framework i8 discharges ore onto a platform 25 from which the fines are'intermittently dropped onto the center of hearth ll by a sweep 21 rotating with shaft 23.

Attached to shell by'suitable brackets not shown are hoppers 38 covered by sloping screens 3|. Cut through the' shell II and also in the upper edge of lining l2 are downwardly sloping I passages or conduits 34 through which fines are passed from drying hearth l'l into hoppers 30. Oversized material discharged by screens 3| is collected by receptacles 32 and conveyed by means not shown to a crusher, or used in a bed roaster or otherwise disposed of. It will be understood the number of conduits 34 and hoppers 30 used-in conjunction with the burner correspend with the number of ore injectors 40 employed. On rotation of rabble arms IS the sulfide fines are gradually fed through. openings 34 into hoppers 30 which discharge fines into injectorfeed pipes '35 having at their lower ends any suitable means such as slide valves 36 for controlling flow of fines out of the lower ends of pipes 35.

The ore injectors 40, shown more or less diagrammatically in the drawing, comprise principally an elongated pipe section or' nozzle 38 constituting a fines inlet conduit. A pipe 39 carrying on the upper end a. funnel 4| is arranged to feed fines into the lower end of nozzle 38. Air or other gas used to inject the fines into the burner is supplied from a bustle pipe 42 surrounding the lower .end of the burner. Bustle 42 may be connected to a blower or other source of air through pipe 43. Adjacent each injector 40, pipe 42 is provided with an air outlet nipple 44 having a control valve 45. Numeral 48 repre-' sents a flexible hose connection attached at one end to nipple-44 and at the other end to jet 41. Each injector unit comprising a nozzle 38, a feed pipe 39 and a funnel- 4| maybe supported by suitable brackets, not shown, in such a way as to permit within certain limits adjustment of the angle between the axes of nozzles 38 and the horizontal and also of theangle between the axes of nozzles 38 and the radii of the combustion chamber. The burner may be provided with any suitable number of injectors. -In the embodiment illustrated, four injectors 40 are employed.

The bottom of the combustion chamber is formed by a hopper-shaped brick hearth 55 terminating in a pit 56 provided with an appropriate conveyor 58 by means of which cinder is discharged from the burner. The upperedge Bl] of brickwork 6| forming the hearth 55 and pit 56 is spaced from the lower edge 62 of the burner proper so as to form a substantially uninterrupted peripheral opening or air inlet 65 communicates with a hopper 30.

the combustion chamber 14 at a point just below crown l5.

The-invention is applicable to the roasting of finely divided metal sulfides such as iron pyrites, pyrrhotite, zinc sulfide or arsenopyrite, but for convenience the operation of the process may be described in connection with the roasting of iron pyrites.

A supply of sulfide fines is maintained in the bin 24 by suitable conveyor or elevator mechanism, not shown. Before roasting is begun, combustion chamber I4 is preheated to temperatures above the ignition point of the particular ore to be roasted, as by the use of oil burners inserted through conveniently located work-holes such as 68, or through the ring-like air inlet 65. When the desired degree of preheat is obtained in the combustion chamber, motor 22 is started, and rabble arms 19 and sweep 21 may be rotated at a rate of, say, one revolution in two minutes. Fines run continuously out of the bin 24 onto platform 25,. and on each revolution of shaft 23 a regulated quantity of ore is swept off the platform to approximately the center of hearth l1. During rotation'of rabble arms l9, the sulfide fines are gradually worked across the surface of hearth l1 and into the several passages 34, each of which The dry or dry and partly preheated fines run into sloping screens 3|, which remove lumps, and thence into hoppers and feed pipes 35.

Valves 36 in pipes are adjusted so that a substantially steady stream of fines runs into the lower ends of nozzles 38 through funnels 4| and pipes 39. Air, steam, or other gas, not adversely affecting oxidation of the sulfides, may be employed to charge the fines into the combustion chamber. For this purpose it is preferred to employ air which may be admitted to the lower ends of nozzles 38.through jets 41 at pressures of, for example, abdut 5 pounds per square inch.

If the ore being roasted is of such nature that extraneous fuel is required to maintain proper roasting temperatures, such fuel in any suitable form may be introduced into the combustion chamber through the ore feed mechanism. For example, a combustible gas might be employed to inject the fines.

The particular angle of the axes of nozzles with the horizontal is dependent upon the particular size and type of combustion chamber which may be employed. The angle of the axes of nozzles ,38, the amount of fines fed into the injectors through pipes 39, and the air pressure in jets 41, adjusted by valves 45, are all regulated with respect to the particular size of the roasting chamber so that the fines particles from each injector rise through the combustion chamber, away from the walls thereof, to an elevation just below the underside of crown l5. The angular position of nozzles 38 (which may be adjusted to suit particular operating conditions) and the rate of supply of ore and air thereto are likewise controlled so that the horizontal travel of the ore accumulation of scar on the walls which tends' to occur when the fines particles while in a state conducive to scar formation are permitted to contact the hot walls of the combustion chamber.

Referring to Fig. 1, the dotted line 12 indicates the approximate path of travel of a fines particle of average size introduced through the injector on the left side of the burner.

Since two or more injectors (in the present 1 instance four) are preferably employed, contacting of fines particles constituting the individual streams fed into the combustion chamber by the separate injectors, breaks up the normal paths of travel of the fines particles so that the drop of the fines from the top to the bottom of the combustion chamber is a substantially straight line fall, or one at a high angle.

In accordance with the present invention, the

roasting operation is carried out so that desulfurization of the fines is substantially completed during the upward flight of the fines particles. To facilitate accomplishment of roasting in this way, the combustion chamber is made vertically elongated in form. In order to obtain the more desirable results, the height of the combustion chamber should exceed the horizontal dimension by not less than about 40% and preferably around Incarrying out the invention, the major portion of the total quantity of air, or other oxidizing gas, necessary to support the oxidation reaction is drawn into the combustion chamber at the bottom through a preferably relatively unobstructed ring-like gas inlet opening 65. Where air is employed for injecting the fines through nozzles 38, not more than about 10% of the total air required for oxidation would ordinarily be introduced through air jets 41, although larger amounts may be used if desired. In the preferred operations, where only a relatively small portion of total air is introduced through the injectors, it may be considered that substantially all the air is introduced into the combustion chamber through inlet 65 and flows upwardly through the furnace. In the particular burner shown in the drawing, the diameter of the combustion chamber is about 16 feet, and the height of the combustion chamber proper from the lower edge 62 of shell I I to crown I5 is about 24 feet. To obtain the best results, the height of the combustion chamber should not be less than about 20 feet. Where the proportions of the combustion chamber are about as stated, the vertical dimensions of opening 65 (i. e., the distance from hearth edge to shell edge 62) may be about 12 inches. If the burner is located in a position where it is exposed to drafts or sudden gusts of wind, shields or drop aprons may be provided around the ring-like gas inlet opening 65 in order to avoid fluctuations in the operation of the burner.

The sulfide fines, dried and more or less. preheated, are injected into the bottom of the combustion chamber, and as substantially all the air for oxidation is drawn in through inlet 65, the fines are initially charged into an atmosphere rich in oxygen. Circular inlet 65 affords uniform admission of air to all points on the lower circumference of the combustion chamber, thus aiding rapid'ignitionof the fines. The atmosphere in the lower 3 or 4 feet of the vertical height of the combustion chamber comprises largely relatively pure air'and hence contains at the most but little sulfur dioxide. Although the atmosphere at and just above the ends of the nozzles is relatively cool because of the introduction of air through circular inlet 65 at about atmospheric temperature, the heating of the upwardly moving ore particles to the ignition tem-' perature takes place rapidly, owing to the absorption of radiant heat fromthe combustion zone. The ore particles are raised to the ignition temperature within a short distance, say from about to about 24 inches from the ends of nozzles 38. Thus, absorption of radiant heat and the presence of an atmosphere uniformly rich in oxygen created by uniform introduction of air through peripheral inlet 65, serve to bring about ignition of fines shortly after introduction into the base of the combustion chamber. I

Following ignition, the fines rise to approximately the top of the combustion chamber, the temperature of the particles increasing because of rapidly progressing roasting. Although the air introduced through circular opening 65 is initially at about normal temperatures, the roasting operation is such roasting atmosphere increases at a rapid, relatively uniform rate'until the temperature of the gases in the top of the-roasting chamber, onentering outlet 10, may be about 1800-2000" F.

Conduit I0 is connected to the inlet side of a blower so that the burner operates under a slight negative pressure.

In accordance with the pitch of nozzles 38, the height of the combustion chamber, the air pressure in jets 41, and the upward fiow of air through the combustion chamber are so adjusted that roasting of the fines particles is substantially complete during the upward flight of the fines while the latter are passing through the combustion chamber co-current with the stream of oxidizing gas. ditions are dependent upon the particular burner in use and may be determined by observation through conveniently located work-holes or by experimental runs if desirable.

described, that bustion chamber is not less than about 20 feet and preferably around 24, desulfurization may be substantially completed before or by the time fines reach the top of the path of vertical movement. 1

0n reaching the upper end of the combustion zone, the substantially completely roasted particles drop through'the combustion chamber at a rate substantially the same as that of similar particles falling under the influence of gravity. In the preferred mode of operation, the fan in gas line I0 is operated so as to draw into the combustionchamber through inlet 65 suflicient oxygen to effect substantially complete oxidation of the fines and also so that the velocity of the rising stream of air through the combustion chamber is substantially less than the initial rate of movement of the fines and not sufficient -to interfere with the free gravity fall of the,

fines. On account of the angular pitch of nozzles 38, and other above-noted control conditions, fines particles during the upward movement, es-

subsequent contact of fines'with thewalls of the combustionchamber is avoided, thus further preventing conditions under which scarring might tend to take place. The iron oxide cinder falling that theltemperature of the.

invention, the angular Such control con- -When working with a burner approximately of the proportions is, where the height of the comthe larger fines particles after reaching residual sulfur on hopper-shaped hearth 55 is finely divided, free-flowing, and runs into pit 56 whence it is removed by the conveyor.

In the furnace of Fig. 1, face of hearth 55 may be considered, for example, as being greater than,the angle of repose of the cinder. 'When this construction is employed. the cinder rolls down the hearth onto conveyor 58 which may be operated at such a rateas to permit a bed of cinder to be built upon the hearth as dotted line 14 represents the upper surface of a bed of cinder, lying at the angle of repose on the hearth, and covering substantially the entire surface of the hearth. .Heat rising from the cinder bed aids in heating air entering through inlet 65and enhances rapid ignition of the fines.

Practice of the invention affords several distinct operating advantages.

the pitch of the sur- Although the major" portion of air used tosupport oxidation of'the;

indicated on the drawing where the fines may be fed into the bottom of the combustion chamber otherwise than through the circular inlet 65 (for-example, a plurality of .circumferentially spaced-apart ports may be used) introduction of air through an uninterrupted openingmakes possible uniform admission of air to all points of the lower circumference of the combustion chamber, consequently aiding in rapid ignition-of the fines. into the bottom of the combustion chamber, effecting roasting during upward flight of the'fines. and withdrawing the sulfur dioxide gases from the top of the combustion chamber, the zone of high sulfur dioxide concentration is maintained in the top of the combustion chamber as far as possibly removed from the cinder discharge opening and air inlet ports in the bottom of the furnace. In practice, the cinder discharge of suspension roasters is in many cases open to the atmosphere. and it often happens that the gas By injecting the finespressure in the roaster more or less momentarily.

changes from a slight minus to a slight plus. in which case substantial volumes d oxide gas puff out through the air inlet and cinder discharge ports and constitute sources of injury to operators and pollution of atmosphere. Occurrences of this nature are minimized by the present invention since the fines particles are substantially completely desulfurized by the time thev reach the top of the combustion chamber, and substant ally all of the sulfur dioxide gas is in the upper end of the combustion chamber remote fromthe air inlet ports and cinder discharge outlet.

Since desulfurization is substantially completed during upward flight, thev combustion chamber, substantially converted to iron oxide. Since the fusion temperature of iron oxide is substantially higher than the fusion on reaching the top of the underside of combustion chamber crown l5, accretion formation thereon is avoided because the fines particles contain substantially no sulfur. Another advantage arising from bottom introduction of the'fines and conducting operations so that desulfurization of the fines is'substantially complete during upward flight and subsequently permitting the fines to drop to the bottom of the combustion chamber is that should some small amount'of sulfur remain in some of the top of the path of movement, such may be oxidized during fall of tlgparticles from I temperature of the iron sulfide fines, even if the particles should strike of strong sulfur the fines particles are p the. top of the combustion chamber through the upwardly flowing air stream so that particles falling on hearth are dead roasted.

The sulfur dioxide gases produced may be used, for example, in the manufacture of sulfuric acid, The sulfur dioxide content of the burner gas .may be regulated as desired by adjusting the amount of air fed into the combustion chamber as is known by those skilled in the art. Gases containing 10-12.5% sulfur dioxide may be readily made by the present process.

In the' above description and in the appended claim, the term fines is intended to designate material of such degree of subdivision as may be roasted while suspended in oxidizing gas. The invention of this application is in some aspects related to the subject matter of my U. S. Patent No. 2,070,236 of February 9, 1937.

' I claim:

The method of roasting finely divided metal sulfides which comprises introducing sulfide fines at the lower periphery of an elongated unobstructed combustion chamber of height sufllcient to permit substantially complete desulfurization of fines while passing from the bottom to the top of said combustion chamber, introducing said fines by means of a stream of gas of such superatmospheric pressure and so directed as to cause said stream of gas to carry the fines upwardly and away from the combustion chamber walls to substantially the top of the combustion chamber and .to cause the fines to pass subsequently downwardly through the combustion chamber while out of contact with the walls of said combustion chamber, introducing into the bottom of the combustion chamber a stream of air in quantity to supply oxygen enough t6 effect roasting of the fines, passing the air stream upwardly through the combustion chamber at velocity less than the initial rate of movement of the fines and not sufficient to substantially interfere with free gravity fall of fines, substantially completely desulfurizing the fines while passing the same to the top of the combustion chamber in co-current fiow relation with the air stream, permitting desulfurized fines to pass downwardly through the combustion chamber, discharging the cinder from the bottom of the combustion chamber, and withdrawing sulfur dioxide gas from the top of the combustion chamber.

' EDWIN J. MULLEN. 

